• 한국표면공학회지
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• 제29권5호
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• pp.487-493
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• 1996

Diamond films were grown at lower temperatures (630-813K) on Si, Al (1100P), and Al-Si(8A, 8B, BC) alloy substrates using improved microwave plasma CVD apparatus in a mixed methane and hydrogen plasma. Improved microwave plasma CVD apparatus equipped water cooled substrate holder and the substrates were set up lower position than bottom line of the applicator waveguide. When the methane concentration was high and growth was conducted at lower pressures the diamond films were synthesized. Moreover the deposits on the scratched substrates formed flat surfaces consisting of fine grains. XRD results, the deposits were identified to cubic diamond. An analysis using Raman spectroscopy, further confirmed that diamond films deposited on the Si substrates were high quality. The deposits on the Al substrates, in contrast, contained amorphous carbon. While the quality of the deposits on the Al-Si substrates were differed with the substrate alloys.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.76-76
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• 2010

Using ab initio density functional calculations, we investigate the structural and electronic properties of porous schwarzite structures formed by $sp^2$ carbon minimal surfaces with negative Gaussian curvature. We calculate the equilibrium geometries, elastic properties and electronic structure of two systems with cubic unit cells containing 152 and 200 carbon atoms, which are metallic and very rigid. The porous schwarzite structure can be efficiently doped by electron donors as well as accepors, making it a promising candidate for the next generation of alkali ion batteries. Furthermore, the schwarzite structures can be magnetic when doped and thus act as arrays of interconnected quantum spin dots. We also propose that two interpenetrating schwarzite structures be used as a ultimate super-capacitor.

• 대한수학회지
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• 제61권4호
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• pp.683-692
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• 2024

Fake projective planes are smooth complex surfaces of general type with Betti numbers equal to that of the usual projective plane. Recent explicit constructions of fake projective planes embed them via their bicanonical embedding in ℙ⁹. In this paper, we study Keum's fake projective plane (a = 7, p = 2, {7}, D₃2₇) and use the equations of [1] to construct an embedding of fake projective plane in ℙ⁵. We also simplify the 84 cubic equations defining the fake projective plane in ℙ⁹.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.47-58
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• 2018

The aim of this work is to investigate the effect of atmospheric stability on near-field pollutant dispersion from rooftop emissions of a single cubic building using computational fluid dynamics (CFD). This paper used the shear stress transport (here after SST) k-${\omega}$ model for predicting the flow and pollutant dispersion around an isolated cubic building. CFD simulations were performed with two emission rates and six atmospheric stability conditions. The results of the simulations were compared with the data from wind tunnel experiments and the result of simulations obtained by previous studies in neutral atmospheric condition. The results indicate that the reattachment length on the roof ($X_R$) obtained by computations show good agreement with the experimental results. However, the reattachment length of the rooftop of the building ($X_F$) is greatly overestimated compared to the findings of wind tunnel test. The result also shows that the general distribution of dimensionless concentration given by SST k-${\omega}$ at the side and leeward wall surfaces is similar to that of the experiment. In unstable conditions, the length of the rooftop cavity was decreased. In stable conditions, the horizontal velocity in the lower part around the building was increased and the vertical velocity around the building was decreased. Stratification increased the horizontal cavity length and width near surface and unstable stratification decreased the horizontal cavity length and width near surface. Maintained stability increases the lateral spread of the plume on the leeward surface. The concentration levels close to the ground's surface under stable conditions were higher than under unstable and neutral conditions.

• 한국지반환경공학회 논문집
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• 제25권5호
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• pp.15-19
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• 2024

본 연구는 대심도 조건에서 고효율 그라우팅 기술 개발을 목표로 하여, 다양한 주입 재료의 적용 가능성을 실험적으로 검증하였다. 1종 보통 포틀랜드 시멘트(OPC)와 마이크로 시멘트(MC)의 입자 크기 분석 및 주입 모형 실험을 통해 각 재료의 주입성능을 평가했다. 국내 대심도 기준, 즉 지하 40미터 이하 조건에서 Barton's Cubic Network 이론을 활용하여 암반 절리 간격을 산정했으며, 선정된 조건에서 입자 크기의 통과 가능성을 분석한 결과, MC는 암반 절리 간격을 통과한 반면, OPC는 간극을 통과하지 못하였다. 실험 장치 및 면적 계산 프로그램을 활용한 주입 모형 실험 결과에 따르면, OPC는 입자 크기가 크기 때문에 주입에 실패한 반면, MC는 고점도 조건에서도 주입이 가능한 것으로 나타났다. 이러한 연구 결과를 바탕으로, 주입 재료에 따른 대심도 조건에서 그라우트 재료의 적용 가능성을 정량적 및 가시적으로 도출하였으며, 고점도 MC 재료는 대심도 암반 절리면 차수 보강에 효과적일 것으로 예상된다.

• Tribology and Lubricants
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• 제35권6호
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• pp.337-342
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• 2019

This paper presents an experimental investigation of friction and wear characteristic with respect to patterns occurring on the surface of 3D printed polymer products by fused deposition modeling method. The purpose of this study was to investigate the effect of the patterns and sliding directions on the tribological properties of 3D printed polymer surface. A cubic specimen was printed using polylactic acid filament as the printing material. Friction tests were conducted for different directions with respect to the patterns that were generated on the top and the side surfaces of the specimen, by using a ball-on-reciprocating type tribotester. SUJ2 bearing ball of which the diameter was 11 times greater than the width of the largest pattern was used as the counter surface to assess the frictional behavior. Friction tests were conducted on the top and the side surfaces with respect to the patterns in 3 (0°, 45°, 90°) different directions respectively. Coefficient of friction increased as cycles increased in all cases. The results of the tests showed that the lowest coefficient of friction was measured with the 45° sliding direction on the side surface. The wear rate was the lowest at 45° sliding direction on the side surface, while it was the highest at 0° sliding direction on the top surface. Coefficient of friction of about 0.45 was determined to be the converging value on the top compared to the side surface.

• 터널과지하공간
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• 제32권6호
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• pp.558-567
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• 2022

고준위방사성폐기물의 지중저장 안정성 평가의 일환으로 가열 중인 화강암의 온도변화와 열응력 발생 양상을 파악하기 위하여 가열실험을 실시하였다. 폐기물의 붕괴열 발생조건을 가정하고 정육면체 형태의 화강암 시편에 적용하여 온도와 변위의 분포를 측정하였다. 시편의 온도는 가열봉에서 발생하는 전도로 인하여 즉각적으로 상승하지만 동시에 외기에 노출되거나 하중재하장치에 접촉되어 있는 표면을 통하여 상당한 양의 열에너지가 소산되었다. 해당 실험에 대한 분석과 이해를 위해 실험조건을 삼차원 유한요소 수치해석으로 재구현하였다. 실험에서 관찰된 열-역학 연계 현상과 주변조건의 변화를 해석에 적용하고 이를 실내실험 결과와 비교하여 검증하였다. 이를 통해 가열실험에 영향을 주는 인자들을 분석하고 향후 관련 연구에서 고려되어야 할 부분을 요약하였다.

• Smart Structures and Systems
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• 제16권5호
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• pp.781-806
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• 2015

A unified formulation of finite layer methods (FLMs), based on the Reissner mixed variational theorem (RMVT), is developed for the three-dimensional (3D) coupled electro-elastic analysis of simply-supported, functionally graded piezoelectric material (FGPM) plates with open- and closed-circuit surface conditions and under electro-mechanical loads. In this formulation, the material properties of the plate are assumed to obey an exponent-law varying exponentially through the thickness coordinate, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the primary field variables of each individual layer, respectively, such as the elastic displacement, transverse shear and normal stress, electric potential, and normal electric displacement components. The relevant orders used for expanding these variables in the thickness coordinate can be freely chosen as the linear, quadratic and cubic orders. Four different mechanical/electrical loading conditions applied on the top and bottom surfaces of the plate are considered, and the corresponding coupled electro-elastic analysis of the loaded FGPM plates is undertaken. The accuracy and convergence rate of the RMVT-based FLMs are assessed by comparing their solutions with the exact 3D piezoelectricity ones available in the literature.

• 한국유체기계학회 논문집
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• 제3권2호
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• pp.7-14
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• 2000

For a given axial turbine blade, reverse design method is developed to improve blade efficiency, optimize blade profile, or repair parts etc. In this process, design parameters for designing axial turbine blade are induced. The induced design parameters are as follows; ellipse at leading edge, radios of trailing edge, axial chord, tangential chord, wedge angle at the inlet, and unguided turning angle. Suction and pressure surfaces of turbine blade are described by cubic polynomials. Two sample blades we chosen and their blade profiles are measured at the mean radius. Values of design parameters for sample blades are obtained by the reverse design method. Re-designed blade profiles using calculated design parameters are compared with the measured data, and they show good agreement. So, the developed design method could be applied to design general turbine blades. Various blade shapes are designed, and they show that designed blade profiles can be adjusted by controlling design parameters.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.406-409
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• 2009

In this work, the magnetite ($Fe_3O_4$)/multi-walled carbon nanotubes (MWNTs) composites for lithium secondary battery were prepared. Nano-$Fe_3O_4$ was deposited by chemical coprecipitation of $Fe^{2+}$ and $Fe^{3+}$ in the presence of MWNTs in alkaline solutions. Transmission electron spectroscopy (TEM) and X-ray diffraction (XRD) analyses indicated that nano-$Fe_3O_4$ particles had a good crystallinity of cubic specimens and many tiny particles attached on the surfaces of the MWNTs. The electrochemical properties of $Fe_3O_4$/MWNTs composites as anodes in lithium-secondary batteries were evaluated by cyclic voltammetry and galvanostatic charge/discharge techniques. The as-prepared $Fe_3O_4$/MWNTs composites showed an initial lithium storage capacity of 1120 mAh/g and a reversible capacity of 394 mAh/g after 100 cycles, demonstrating better performance than that of the commercial graphite anode materials.